Division of Energy
Global Climate Change: Stratospheric Ozone
Man-made chlorinated (and brominated) chemicals such as refrigerants, freons, and degreasers provide the foundations for the diminishing levels of stratospheric ozone. The more common of these chemicals, chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's), halons, and 1,1,1 trichloroethane (methyl chloroform) are emitted through many industrial and commercial processes such as metal degreasing, servicing air conditioning equipment, cleaning electronic components, and even firefighting. Their popularity as chemicals comes in their minimal toxicity, low flammability, great heat transfer capacity, and tremendous stability. Many of these compounds are so stable they can remain in the atmosphere for up to 400 years. Atmospheric diffusion will eventually raise them to the stratosphere. It's in the stratosphere where these compounds finally destabilize and trigger the ozone destruction process.
The Ozone Depletion Process
The stratospheric ozone layer itself is created and maintained by a balanced dynamic process. Varying wavelengths of ultraviolet radiation from the sun continually reproduce and destroy ozone 10 to 30 miles above the surface. When unnatural amounts of chlorine and bromine reach the stratosphere, they also react to the ultraviolet light. This chlorine/ultraviolet reaction breaks the compounds into smaller and more basic components. Chlorine (C1- ) and chlorine monoxide (ClO) are the components of most concern because they react with ozone (O3). This reaction sequence (Cl+O3=ClO+O2 and ClO+O=Cl+O2) splits the ozone into oxygen components of O2- and O2. This process can repeat itself over and over in a chain reaction destroying thousands of ozone molecules. What was a naturally balance cycle of ozone production and destruction is now tipped in favor of destruction.
This chlorine/ozone reaction, however, is not sufficient enough to cause the level of ozone depletion that has occurred over the past 10 years. The ozone destruction process is accelerated by the extreme cold of "polar stratospheric clouds," which are made primarily of ice crystals, that develop at the two poles. These cloud "particles" trap the chlorinated compounds during the cold, dark winters. Then, as spring approaches with the rising sun, these clouds warm up and begin to dissipate, releasing large amounts of the chlorinated compounds that react quickly with the sun's ultraviolet rays and begin the ozone destruction sequence. As the ozone layer continues to thin each year, the polar stratospheric clouds break up later and layer and layer allowing more exposure of the compounds to ultraviolet rays. As a result, the ozone "hole" has increased almost every year, diminishing the total level of ozone in the stratosphere between 4 and 8 percent over the past decade.
Effects of Ozone Depletion
The destruction of ozone in the stratosphere means that more ultraviolet radiation will reach Earth's surface. The consequences are many and in most cases negative. Humans are affected directly by increased radiation which accelerates aging and wrinkling of the skin, increases acute cases of sunburn, and escalating occurrences of skin cancer. Cataracts will become more frequent and they can lead to blurred vision and eventual blindness. Ultraviolet radiation will reduce the immune system's ability to fight off germs and microorganisms and elevate the body's susceptibility to disease.
Some scientists believe that the widespread decline of certain amphibians (e.g., frogs and salamanders) may be due to the effect of increased ultraviolet radiation on their eggs. Humans are also affected indirectly through the food chain. The photosynthesis process is disrupted by ultraviolet radiation increasing crop aging rates, "burning" of crops, and lower yields. Slower plant growth will affect habitation and wildlife. And at the most basic level, the growth of phytoplankton will be suppressed, which is the basis for the ocean food chain. Materials such as paints, plastics, coatings, and framework also will show increased aging degradation.
Most of the ozone depleting chemicals are being phased out. CFC'c, methyl chloroform, and halons will be banned from being manufactured in the United States by 1996. Many companies already are substituting HCFC'c and HFC'c (hydrofluorocarbons) where they once used CFC's. HCFC's have an ozone depletion rate that is a fraction of CFC's. HFC'c have no ozone depletion potential at all. Federal regulations now require recycling of refrigerants and repair of leaking systems. In the process, new environmentally safe products and procedures are being developed every day. The direction in the United States is positive, with much of the industrialized world following suit. Is it too little too late? Maybe. The majority of ozone depleting chemicals have yet to reach the stratosphere.
Continued depletion of our plant's protective ozone layer will not only lead to changes in lifestyle, but more importantly, to changes in the world's ecosystem. All aspects of human and animal life could be affected by disruptions in food chain and plant life elements caused by ultraviolet radiation. This will be devastating to thousands of species and yet cause other more resilient species to flourish.
Whenever we develop new chemicals or substances we must take care to investigate hoe their use interacts with what already exists.